This invention relates to a plant malfunction diagnostic method for sensing a malfunction and identifying the cause thereof in a plant such as a nuclear power station or thermal power plant in which there are a large number of parameters to be monitored and the parameters are interrelated in a complicated manner.
Plants such as nuclear power stations or thermal power plants generally use a large number of announciators adapted to issue an alarm to inform the operators of the occurrence of a malfunction if a level of plant state variable exceeds a predetermined limit value. For example, in a nuclear power plant or the like, the number of announciators can be as many as several thousand, and a large number of lamps can flash in the occurrence even of a minor accident. Hence, it is difficult for an operator to be supplied solely with the information necessary. Consequently, various countries are developing systems for diagnosing malfunctions by utilizing computers. Typical systems are the nuclear power generating support system of Japan, the Gesellschaft fur Reaktorischerheit (GRS) of West Germany, the STAR being developed by the Halden project of Norway, and the DAS being developed by commission of the EPRI (the Electric Power Research Institute of the United States).
A malfunction diagnostic method referred to as cause consequence Tree (CCT) is employed in these systems. For example, in accordance with CCT, the relationship between the causes of malfunctions and their consequences is represented in the form of a tree. When a malfunction occurs, the state of its consequence is observed and the branches of the tree are traversed in the reverse direction to arrive at the cause. Ordinarily, retrieval by CCT starts at the beginning of operation of an announciator set to a level which is .+-.10-20% of a plant state variable under power operation. Therefore, after the occurrence of a malfunction which propagates rapidly in tens of seconds, the possibility arises that the operator may not be able to perform the proper recovery operation.